The study will be initiated in September 1977, with 1200 children in the seventh grade of seven junior high schools located in Des Moines, Iowa, a community that has optimal amounts of fluoride in its supply of drinking water. Following base line dental examinations, in which the DMF surface index will be used, the children will be randomly assigned to one of the following three study groups: Group I (controls) will rinse their mouths once every week in school for 60 seconds with a placebo solution; Group II will follow an identical procedure using a 0.2% neutral sodium fluoride solution (0.09% F); Group III will rinse their mouths once every day in school for 60 seconds using a 0.05% neutral sodium fluoride solution (0.023% F). The procedures will be carried out under the classroom teacher's supervision for a period of three years. Follow-up examinations will be conducted in October 1978, October 1979 and May 1980.